While most organic beauty products have a clearly marked expiration date (as they don't contain preservatives), the Times reports today that most standard cosmetics don't, even though ingredients lose their effectiveness over time and containers become a petri dish for bacteria.
Right now, there are no set rules for how cosmetics should be labeled. And while many of our favorite lotions and potions have a "use-by" date, a standard for how companies arrive at that date does not exist. But until the industry comes together and figures this out, here's a simple solution: Look for the little jar picture, which we've illustrated above and is usually found on the back of the outer packaging. The number, which seems like it might be a metric weight, is actually a suggested length of time the product should be kept in your makeup bag starting from the day you open it. Mind blown, or what?